In recent years, a phenomenon has been discovered in which certain metal oxide materials have two states of a low resistance state and a high resistance state when a voltage is applied due to the resistivity prior to the application of the voltage and the amount of the voltage; and a new nonvolatile memory device utilizing this phenomenon is drawing attention. Such a nonvolatile memory device is referred to as a ReRAM (Resistance Random Access Memory). From the viewpoint of higher integration, a three-dimensional cross-point structure has been proposed as an actual ReRAM device structure in which memory cells include pillars formed at intersections between word lines (WL) and bit lines (BL) and include a resistance change layer and a diode layer stacked in the pillar.
However, while it is necessary to use finer pillars for higher integration of the memory cells, finer pillars have higher aspect ratios; and the formation of the pillars is unfortunately difficult in a ReRAM having such a three-dimensional cross-point structure.